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Abstract

Abstract

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Abstract

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  1. Abstract To increase the mapping speed, a focal plane array (FPA) receiver is considered for the Submillimeter Array (SMA). Current development of 7-pixel optics designs at the key observing frequency of 345GHz is presented. Five trials were attempted using relay optics (RO) of different configurations. The best solution is a FPA with two off-axis ellipsoidal mirrors as RO. It has anoff-axis beam efficiency 79%, compared to 84% with the original SMA optics. 7 pixels are spaced 45mm apart, and the field of view (FOV) reaches 5.5’. Conclusion & Future Task Among 5 trials for multi-pixel optics design for the SMA, the configuration with 2 off-axis ellipsoidal mirrors have the best beam efficiency of 7 pixels. Detailed design of RO and receiver based on the trial#5 will follow, taking into account the related constraints of the receiver cabin and the current 300 GHz receiver design. The largest possible pixel number and the largest FOV will also be studied by designing a realistic multi-pixel receiver using the current 300 GHz receiver. Trial#5 This solution adds two off-axis ellipsoidal mirrors as RO, and keep the feed-to-subreflector distance identical to that of the original optics. Off-axis beam efficiency varies from 75-79% due to beam distortion by the ellipsoidal reflectors. Fig. 3 Optics of Trial#5. Optics Design Highlights 5 trials of 7-pixel optics were designed using quasi optics techniques and verified in physical optics simulation software GRASP. Trial#1 Using the original RO and the 300 GHz receiver, this solution put together 7 feedhornsand a lensletarray in a hexagonal arrangement. Insert lenses were reduced from 70mm to 25mm in diameter (0.9 beam radius), so that all pixels pass through cryostat window (76mm in diameter). Simulation showed that lens truncation reduced beam efficiency by 30%. Trial#3 This solution is a FPA without RO, which places the beam waist of the insert lens/feedhorn combination at the Cassegrain focal point. Off-axis Gaussian beams were completely reflected by the secondary mirror when feeds were spaced 45mm apart. The off-axis beam efficiency is 78%, comparable to 81% of the on-axis beam. Fig. 4: Co-polarization (left) and cross-pol (right) of on-axis beam of trial#5. Fig. 5: Co-polarization (left) and cross-pol (right) of one off-axis beam of trial#5. Fig 1. Trial#1 simulated in GRASP. The Blue tube is the Gaussian beam, and the olive aperture is the cryostat window. Multi-Pixel Optics Design for the Submillimeter ArrayYun-Chih Chou, Chao-Te Li, Ming-Tang Chen Table 1. Beam efficiency of 5 trials simulated using GRASP. Beam efficiency was integrated down to 12dB below peak value. Fig. 2 Trial#3 optics. Blue region is one off-axis Gaussian beam tube; magenta rays are center rays of 7 feeds. 2013/3/20

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